The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a brushless direct current (BLDC) motor, which is a motor formed by replacing a commutator and a brush, which are in mechanical contact with each other, in a DC motor having an electronic rectifying unit, has the advantages of low electromagnetic noise and mechanical noise and a long lifespan. As devices have been increased in performance, reduced in weight and thickness, simplified in structure, and increased in lifespan and parts or materials for semiconductor technology have been developed, the brushless direct-current motor has made great strides and has been used in various fields such as home appliances, information communication devices, vehicles, and medical equipment.
Such brushless direct current motor generally includes rotors, which are permanent magnets, and a stator, which is a fixed wound wire, particularly a three-phase stator. The position of the rotor is detected by a position sensor such as a hall sensor and voltage is repeatedly and alternately applied to the stators, depending on the detected position of the rotor, whereby the brushless direct-current motor is operated.
When the rotor rotates and the brushless direct-current motor is operated, the same effect as when a wire moves in a magnetic field is produced. And, a counter electromotive force, which is an induced electromotive force, is generated in the stators, so a current flows in the stators with a voltage corresponding to the difference between the counter electromotive force and an applied voltage.
Accordingly, for a desired operation of a brushless direct-current motor, voltage should be repeatedly and alternately applied to the stators, that is, the phases of the stators should be changed, simultaneously with signal detection of the hall sensor. However, the point of time at which a wire current flows in the stators is delayed relatively, compared to the point of time at which the phases of the stators are converted due to the influence of wire inductance of the motor. In particular, the larger the inductance and the higher the rotational speed of the motor, the larger the delayed angle of a phase current, which may cause reduction in efficiency and torque of a brushless direct-current motor.